1. Field of the Invention
This invention relates to the production of composite safety glass by unilateral or bilateral bonding of one of more silicate glass panes to a plasticized soft film of an ethylene or propylene mono-, co- or terpolymer. More especially, this invention is directed to the manufacture of laminated safety glass by the bonding together of one or more sheets of silicate glass to a soft film of a polymer of ethylene or propylene.
2. Discussions of the Prior Art
There are many applications for laminated safety glass. It is used, for example, in the building industry for the production of doors or windows, bullet-proof glass and skylights, and in the automotive industry especially for the manufacture of windshields.
The term "laminated safety glass", as used herein, is to be understood to means a sandwich consisting of one or more silicate glass sheets bonded together in one unit with a film of organic material. If the glass is broken, the fragments adhere to the film. Loose, sharp-edged splinters are not formed (cf. DIN 1259, Sheet 2).
Laminated safety glass must satisfy certain quality requirements according to the purpose for which it is to be used. In the case of motor vehicles, these quality requirements are laid down in the "Strassenverkehrszulassungsordnung" of the German Federal Republic, Section 22, No. 29, in "Motor Vehicle Safety Standards" Nos. 205 and 208, and in U.S.A. Standard Z 26.1-1966. Quality requirements for use in the building industry are established in "American National Standard Institute" Standard Z 97.1-1966, and for use as bullet-proof material they are specified in "Underwriters Laboratories" Standard 752.
In practice, the use of laminated safety glasses on the basis of silicate glass sheets bonded together with films of plasticized polyvinyl butyral has become widespread. However, the use of polyvinyl butyral films containing plasticizers makes the production of laminated safety glass very expensive.
Polyvinyl butyral films cannot generally be manufactured on the commonly available equipment such as is used for the production of other plastic films, and apparatus especially designed for this type of film must be used not only for the production of such films, but also for their incorporation into laminated safety glass. Certain special requirements must be satisfied. For example, the films have to be adjusted to certain specific moisture contents and to precise free hydroxyl group contents in order that the optimum adhesive strength desired for the particular application can be consistently achieved. On account of their sensitivity to moisture, polyvinyl butyral films must be handled under controlled atmospheric conditions in most cases, not only during their manufacture and storage, but also immediately prior to their incorporation into the laminated safety glass. It is also disadvantageous that polyvinyl butyral film containing plasticizer sticks to itself and therefore must first be provided with a parting means if they are to be stored or transported in the form of stacks of die-cut blanks or in the form of rolls.
It has been proposed to replace the plasticized polyvinyl butyral film with other organic adhesive materials. For example, it is proposed in German No. "Offenlegungsschrift" 1,421,142 that films of highly polymerized vinyl chloride be used as fire-retardant intermediate layers, to which vinyl chloride of a low degree of polymerization (K values under 50, preferably between 30 and 40) has been added for the achievement of adhesion to glass. The low polymers can also be applied to the surfaces of the glass sheets in the form of a thin, viscid coating before they are joined together. With adhesive films of this kind, approximately the same problems are encountered as in the preparation and use of polyvinyl butyral films.
In co-pending application Ser. No. 738,402, the disclosure of which is hereby incorporated by reference, it is proposed to obviate the afore-mentioned problems by employing as the film to which the silicate glass layers are bonded a plasticized polyvinyl chloride film. It has been discovered, in accordance with our invention as disclosed therein, that improved adhesion and shatter resistance are provided using a plasticized polyvinyl chloride film. The strength of adhesion is remarkably superior, according to the procedure therein, than has been obtained heretofore for composite safety glasses utilizing polyvinyl butyral. It has become desirable, however, to provide other forms of composite safety glass employing films other than those containing polyvinyl chloride. It has become particularly desirable to provide composite safety glass which is not only useful in the vehicle sector, but can be used in the construction sector as well for window panes, bullet-proof glass, window railings, partitions and the like. It has become especially desirable to provide such laminated safety glass which can take advantage of the properties of other synthetic resin films.